1. Field of the Invention
The present invention is directed to a process for decomposing ammonia and more specifically a process for the selective decomposition of ammonia to nitrogen in an ammonia containing off-gas at low temperatures in the presence of a catalyst.
2. Description of the Related Art
Catalytic decomposition of ammonia with oxygen to nitrogen and water proceeds at the following reaction: EQU 4NH.sub.3 +30.sub.2 .fwdarw.2N.sub.2 +6H.sub.2 O
In addition to the above oxidation reaction, ammonia further reacts with oxygen to nitrogen oxides mainly by the reaction: EQU 4NH.sub.3 +70.sub.2 .fwdarw.4NO.sub.2 +6H.sub.2 O EQU 4NH.sub.3 +50.sub.2 .fwdarw.4NO+6H.sub.2 O EQU 2NH.sub.3 +20.sub.2 .fwdarw.N.sub.2 O+3H.sub.2 O
For reasons of high formation of desired nitrogen, the process depends substantially on the selectivity of a decomposition catalyst for the formation of nitrogen as the main oxidation product rather than the undesired nitrogen oxides.
Known catalysts being active in the selective decomposition of ammonia are cobalt or cobalt oxide containing catalysts as described in German Offenlegungsschrift No. 2,026,657, and vanadium oxide containing catalysts supported on a carrier of alumina as disclosed in U.S. Pat. No. 5,139,756. Other known catalysts for the decomposition of ammonia in the lower temperature range contain platinum metals (German Offenlegungsschrift No. 2,447,552).
We have now found that selectivity and activity of the known ammonia decomposition catalysts are, surprisingly, improved when sulfating the catalysts during or prior to contact with ammonia containing gas.